In the mosquito, trophocytes of the fat body are involved in a massive production of protein yolk precursor(s). Trophocytes undergo cyclic activity in three successive stages: (1) proliferation of biosynthetic organelles, (2) synthesis of yolk precursor(s), and (3) lysosomal breakdown of the biosynthetic apparatus. The research proposed here concerns the elucidation of the mechanisms that coordinate the cyclicity of trophocyte activities. The activation of trophocyte nucleoli and a massive proliferation of ribosomes is the most pronounced event of the first stage. We intend to determine the developmental course of ribosomal production and investigate what factors turn on and off this process. We have obtained a library of monoclonal antibodies (mAB) against components of protein yolk. One group of mAB recognizes vitellin and its precursor, vitellogenin, in the fat body. The second group of mAB is specific for a smaller protein, which is present in the protein yolk and also originates in the fat body. The most important part of this proposal will be the characterization of mABs and the development of specific molecular probes for studying the fat body precursors of these components of protein yolk. We found that the lysosomal system plays an important role in the cyclicity of trophocyte activity by degrading the biosynthetic apparatus during the cessation of VG production. We want to know whether a high titre of VG (feedback control) or hormonal factor (oostatic hormone) stimulates this lysosomal activity. Further, we want to learn whether this specific lysosomal activity is physiologically linked to the end of VG synthesis, or if it can be stimulated independently at any time during VG synthesis. This proposal will provide important information about the process which, in mosquitoes and other insects, is a cornerstone of egg maturation and it will move us closer in the search for new approaches to the control of this important arthropod vector.